(IL)Intermediate Language is also known as MSIL (Microsoft Intermediate Language) or CIL (Common Intermediate Language). All .NET source code is compiled to IL. This IL is then converted to machine code at the point where the software is installed, or at run-time by a Just-In-Time (JIT) compiler.

What is a CLR?

CLR (Common Language Runtime) is the heart of the .NET framework. All Languages have runtime and its the responsibility of the runtime to take care of the code execution of the program. For example Java has JVM(Java Virual Machine) Similarly .NET has CLR.

Code Access Security : CAS grants rights to program depending on the security configuration of the machine. Example the program has rights to edit or create a new file but the security configuration of machine does not allow the program to delete a file. CAS will take care that the code runs under the environment of machines security configuration.

IL(Intermediate language)-to-native translators and optimizer's : CLR uses JIT and compiles the IL code to machine code and then executes. CLR also determines depending on platform what is optimized way of running the IL code.

What is a CTS?

In order that two language communicate smoothly CLR has CTS (Common Type System). Example in VB you have "Integer" and in C++ you have "long" these data types are not compatible so the interfacing between them is very complicated. In order to able that two different languages can communicate Microsoft introduced Common Type System. So "Integer" datatype in VB6 and "int" datatype in C++ will convert it to System.int32 which is datatype of CTS.

What is a CLS?

Common Language Specification is a subset of the CTS which all .NET languages are expected to support. It was always a dream of Microsoft to unite all different languages into one umberlla and CLS is one step towards that. Microsoft has defined CLS which are nothing but guidelines that language to follow so that it can communicate with other .NET languages in a seamless manner.

What is Managed Code?

Managed Code runs inside the environment of CLR i.e .NET runtime. In short all IL are managed code. But if you are using some third party software example VB6 or VC++ component they are unmanaged code as .NET runtime (CLR) does not have control over the source code execution of the language.

What is a Assembly?

Assembly is unit of deployment like EXE or a DLL.
An Assembly consists of one or more files (dlls,exe's,html files etc.) and represents a group of resources, type definitions, and implementations of those types. An assembly may also contain references to other assemblies. These resources, types and references are described in a block of data called a manifest. The manifest is part of the assembly, thus making the assembly self-describing.
An assembly is completely self-describing. An assembly contains metadata information, which is used by the CLR for everything from type checking and security to actually invoking the components methods. As all information is in the assembly itself, it is independent of registry. This is the basic advantage as compared to COM where the version was stored in registry.
Multiple versions can be deployed side by side in different folders. These different versions can execute at the same time without interfering with each other. Assemblies can be private or shared. For private assembly deployment, the assembly is copied to the same directory as the client program that references it. No registration is needed, and no fancy installation program is required. When the component is removed, no registry cleanup is needed, and no unistall program is required. Just delete it from the hard drive.
In shared assembly deployment, an assembly is installed in the Global Assembly \ Cache (or GAC). The GAC contains shared assemblies that are globally accessible to all .NET applications on the machine.

What are the different types of Assmbly?

There are two types of assembly Private and Public assembly. A private assembly is normally used by a single application, and is stored in the application's directory, or a sub-directory beneath. A shared assembly is normally stored in the global assembly cache, which is a repository of assemblies maintained by the .NET runtime. Shared assemblies are usually libraries of code which many applications will find useful, e.g. Crystal report classes which will be used by all application for Reports.

What is Namespace?

Namespace has two basic functionality :
Namespace Logically group types, example System.Web.UI logically groups our UI related features.
In Object Oriented world many times its possible that programmers will use the same class name. By qualifying Namespace with clasname this collision can be avoided.

Assembly metadata is stored in Manifest. Manifest contains all the metadata needed to do the following

Version of Assembly
Security identity
Scope of the assembly
Resolve references to resources and classes
The assembly manifest can be stored in either a PE file(an .exe or .dll) with Microsoft intermediate language (MSIL) code or in a stand-alone PE file that contains only assembly manifest information.